Chronic diseases are often expressed by episodic worsening of clinical symptoms. Preventive treatment of chronic diseases reduces the overall dosage of required medication and associated side effects. Generally, preventive treatment should be initiated or intensified as soon as the earliest clinical symptoms are detected, in order to prevent progression and worsening of the clinical episode and to stop and reverse the pathophysiological process. Therefore, an ability to accurately monitor pre-episodic indicators increases the effectiveness of preventive treatment of chronic diseases.
Many chronic diseases interfere with normal breathing patterns, through a variety of physiological mechanisms. Common respiratory disorders, such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), are direct modifiers of breathing patterns. Other chronic diseases, such as diabetes, epilepsy, and certain heart diseases, are also known to modify breathing activity, because of pathophysiologies leading to abnormal sympathetic and parasympathetic neural activity.
Asthma is a chronic disease with no known cure. Substantial alleviation of asthma symptoms is possible via preventive therapy, such as the use of bronchodilators and anti-inflammatory agents. Asthma management is aimed at improving the quality of life of asthma patients. Asthma management presents a serious challenge to the patient and physician, as preventive therapies require constant monitoring of lung function and corresponding adaptation of medication type and dosage. However, monitoring of lung function is not simple, and requires sophisticated instrumentation and expertise, which are generally not available in the non-clinical or home environment.
Monitoring of lung function is viewed as a major factor in determining an appropriate treatment, as well as in patient follow-up. Preferred therapies are based on aerosol-type medications to minimize systemic side-effects. The efficacy of aerosol type therapy is highly dependent on patient compliance, which is difficult to assess, further contributing to the importance of lung-function monitoring.
Asthma episodes usually develop over a period of several days, although they may sometimes seem to appear unexpectedly. The gradual onset of the asthmatic episode provides an opportunity to start countermeasures to stop and reverse the inflammatory process. Early treatment at the pre-episode stage may reduce the clinical episode manifestation considerably, and may even prevent the transition from the pre-clinical stage to a clinical episode altogether.
Two techniques are generally used for asthma monitoring. The first technique, spirometry, evaluates lung function using a spirometer, an instrument that measures the volume of air inhaled and exhaled by the lungs. Airflow dynamics are measured during a forceful, coordinated inhalation and exhalation effort by the patient into a mouthpiece connected via a tube to the spirometer. A peak-flow meter is a simpler device that is similar to the spirometer, and is used in a similar manner. The second technique evaluates lung function by measuring nitric-oxide concentration using a dedicated nitric-oxide monitor. The patient breathes into a mouthpiece connected via a tube to the monitor.
Efficient asthma management requires daily monitoring of respiratory function, which is generally impractical, particularly in non-clinical or home environments. Peak-flow meters and nitric-oxide monitors provide a general indication of the status of lung function. However, these monitoring devices do not possess predictive value, and are used as during-episode markers. In addition, peak-flow meters and nitric-oxide monitors require active participation of the patient, which is difficult to obtain from many children and substantially impossible to obtain from infants.
Congestive heart failure (CHF) is a condition in which the heart is weakened and unable to circulate blood to meet the body's needs. The subsequent buildup of fluids in the legs, kidneys, and lungs characterizes the condition as congestive. The weakening may be associated with either the left, right, or both sides of the heart, with different etiologies and treatments associated with each type. In most cases, it is the left side of the heart which fails, so that it is unable to efficiently pump blood to the systemic circulation. The ensuing fluid congestion of the lungs results in changes in respiration, including alterations in rate and/or pattern, accompanied by increased difficulty in breathing and tachypnea.
Quantification of such abnormal breathing provides a basis for assessing CHF progression. For example, Cheyne-Stokes Respiration (CSR) is a breathing pattern characterized by rhythmic oscillation of tidal volume with regularly recurring periods of alternating apnea and hyperpnea. While CSR may be observed in a number of different pathologies (e.g., encephalitis, cerebral circulatory disturbances, and lesions of the bulbar center of respiration), it has also been recognized as an independent risk factor for worsening heart failure and reduced survival in patients with CHF. In CHF, CSR is associated with frequent awakening that fragments sleep, and with concomitant sympathetic activation, both of which may worsen CHF. Other abnormal breathing patterns may involve prolonged expiration or inspiration, or gradual changes in respiration rate usually leading to tachypnea.
U.S. Pat. No. 5,853,005 to Scanlon, which is incorporated herein by reference, describes a transducer in communication with fluid in a pad. The pad is held in close contact against a sound or movement source, and monitors acoustic signals transferred into the fluid. The signal pattern is monitored aurally and/or compared to predetermined reference patterns, and optional control and stimulation means can be activated in response to the comparison results. The sensed acoustic signal can be transmitted to a remote receiver or processed locally. Typically, the acoustic signal is representative of the heartbeat or breathing of a living organism. The monitoring system may be applied to diverse situations including SIDS, apnea, home baby monitoring, medical transport devices, blood pressure cuffs, seats, combat casualty care and hand-held devices. An embodiment is described in which the system is attached to home or institution mattresses for health monitoring, recovery, research, or presence detection.
U.S. Pat. No. 6,666,830 to Lehrman et al., which is incorporated herein by reference, describes a system for detecting the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops, and before the cessation of breathing occurs. The system includes one or more microphones capable of detecting breathing sounds within an airway of a person. The microphones generate signals representative of the breathing sounds, and send the signals to a controller. The controller identifies at least one signal pattern that is associated with a breathing pattern of the person that occurs at the onset of an obstructive sleep apnea event. The controller may also identify at least one signal pattern that is associated with a partially-occluded breathing pattern of the person. The controller identifies the signal patterns by using digital signal processing techniques to analyze the signals representative of breathing sounds. The method involves detecting breathing sounds within an airway of a person, generating signals representative of the breathing sounds, and identifying at least one signal pattern that is associated with a breathing pattern of the person that occurs at the onset of an obstructive sleep apnea event.
U.S. Pat. No. 6,790,183 to Murphy, which is incorporated herein by reference, describes a lung sound diagnostic system for use in collecting, organizing and analyzing lung sounds associated with the inspiration(s) and expiration(s) of a patient. The system includes a plurality of transducers that may be placed at various sites around the patient's chest. The microphones are coupled to signal processing circuitry and A/D converters which digitize the data and preferably provides the digital data to a computer station. The system may also include application programs for detecting and classifying abnormal sounds. The resulting information may be displayed in a variety of formats to facilitate diagnosis. Additionally, the system may include an analysis program for comparing selected criteria corresponding to the detected abnormal sounds with predefined thresholds in order to provide a likely diagnosis. Also described are a system and method for differentiating between the crackles produced by an patient with interstitial pulmonary fibrosis (IPF) from the crackles produced by a CHF patient.
U.S. Pat. No. 6,168,568 to Gavriely, which is incorporated herein by reference, describes a phonopneumograph system for analyzing breath sounds. The system includes a plurality of breath-related sensors placed around the respiratory system of a patient for measuring breath-related activity, and a breath analyzer. The breath analyzer matches the breath sound data produced by the breath-related sensors to a plurality of breath sound templates, each of which parameterizes one type of breath sound, and determines the presence of regular and/or adventitious breath sounds only when the breath sound data matches, within predetermined goodness of fit criteria, one or more of the breath sound templates.
U.S. Pat. No. 6,261,238 to Gavriely, which is incorporated herein by reference, describes a method for analyzing breath sounds produced by a respiratory system. The method includes measuring breath sounds produced by the respiratory system; tentatively identifying a signal as being caused by a breath sound of a given type if it meets a first criterion characteristic of the breath sound of the given type; and confirming the identification if a tentatively identified signal meets a second criterion characteristic of the breath sound of the given type.
U.S. Pat. No. 5,738,102 to Lemelson, which is incorporated herein by reference, describes a system for monitoring and computer analyzing select physiological variables of a patient in real time in order to alert medical personnel to the need for medical treatment or automatically administering such treatment under computer control. Such physiological variables monitored by the system may include lung sounds, respiratory rate and rhythm, heart rate and rhythm, heart sounds, and body temperature. Coded signals relating to the physiological variables are produced and compared with reference versions of same by a decision computer in order to evaluate the patient's condition. If the evaluation indicates medical treatment is needed, the decision computer activates a local and/or a remote alarm to alert medical personnel and/or activates one or more actuators for administering a medical treatment such as the injection or infusion of a drug.
An article by Shochat M et al., entitled, “PedemaTOR: Innovative method for detecting pulmonary edema at the pre-clinical stage,” undated, available at http://www.isramed.info/rsmm_rabinovich/pedemator.htm, which is incorporated herein by reference, describes an impedance monitor for pre-clinical detection of pulmonary edema. The impedance monitor measures “internal thoracic impedance” (ITI), which is roughly equal to lung impedance, by automatically calculating skin-electrode impedance and subtracting it from the measured transthoracic impedance (TTI).
The following articles, which are incorporated herein by reference, may be of interest:    Bentur L et al., “Wheeze monitoring in children for assessment of nocturnal asthma and response to therapy,” Eur Respir J 21(4):621-626 (2003).    Stegmaier-Stracca P A et al., “Cough detection using fuzzy classification,” Symposium on Applied Computing, Proceedings of the 1995 ACM Symposium on Applied Computing, Nashville, Tenn., United States, pp. 440-444 (1995).    Waris M et al., “A new method for automatic wheeze detection,” Technol Health Care 6(1):33-40 (1998).
The inclusion of the foregoing references in this Background section does not imply that they constitute prior art or analogous art with respect to the invention disclosed herein.